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Slurry: The Risks and Necessary Precautions

When managed appropriately, slurry is a very valuable asset on any farm, but it also comes with its risks. Slurry spreading is a conventional method of returning nutrients to the soil. In Ireland, over 40 million tonnes of slurry are stored, handled, and spread each year. It is important to remember that these are extremely dangerous activities if not managed safely. Incidents such as drowning in slurry and water, as well as gas poisoning, have claimed several lives in Ireland and Northern Ireland. Many of these tragic accidents were also caused by the release of dangerous gasses during the mixing of slurry. Hundreds of livestock have also died in these circumstances. 

There are three key safety issues farmers must consider when handling slurry. These are 

  1. Slurry gases
  2. Slurry tank openings
  3. The slurry tanker and the Power Take Off (PTO)

Slurry Gases

Several hazardous gases are released during the bacterial decomposition of slurry in tanks. Inhaling these gases – which can include hydrogen sulphide, ammonia, methane and carbon dioxide – can be lethal. All these gases are heavier than air, so they displace oxygen. This can lead to suffocation when a person enters a tank. In particular, hydrogen sulphide is extremely poisonous both to people and livestock, and there have been many incidents where they have been killed by this toxic gas. Hydrogen sulphide affects the nervous system, and even small concentrations can cause death. Poisoning occurs above ground due to the release of hydrogen sulphide, which is more poisonous than hydrogen cyanide, the poison gas used in World War1. Hydrogen Sulphide can be detected by smelling at 0.1 ppm, but at 150 ppm the olfactory nerve which detects smell in the nose is desensitised, and it then cannot be detected by smell. The gas produces adverse health effects at increasing concentration and is rapidly fatal above 700ppm.

During agitation, the emission of this gas is at its highest. This occurs in the following instances: in the first 30 minutes of agitation, when the slurry has been stored for several months, when it is agitated in deep tanks and after silage effluent has been added. 

When agitating slurry, it is advised that at least two people are present at all times and always make sure that children are not nearby. Farmers must follow the below guidelines when agitating slurry. 

  1. Choose a windy day, to help disburse the dangerous gases that are released during agitation, and open all doors and outlets. A wind speed of at least Beaufort Scale 2, where wind is felt on exposed skin, leaves rustle and has a speed of 7 km/h or higher, is required as this rapidly dissipates the poisonous gas.
  2. With sheds, ensure that all doors and vents are opened and that there is adequate air movement. Ensure all persons, particularly children or the elderly, do not enter during/after agitation. Installing a slurry aeration system is an alternative to handling and mixing slurry indoors.
  3. Teagasc guidance does not recommend the use of gas detection systems by farmers. These meters typically are set to alarm at 10ppm, which is the Occupational Exposure Limit Value (OELV) for a 15-minute exposure under the Code of Practice for the Safety, Health and Welfare (Chemical Agents) Regulations. This is considered to be the maximum exposure that will not cause a health issue.
  4. The problem is that with the potentially high level of hydrogen sulphide emissions from slurry (over 1000ppm), a fatality could occur instantly. The best advice is that gas detection systems can only be used safely along with full breathing apparatus, and that they should not be used as a substitute for the safety guidelines outlined above.
  5. Entering a slurry tank or any tank with organic material in it can be lethal and is not advised. Doing this work is covered by Confined Space entry regulations, and a Code of Practice giving guidance on these regulations is available on the HSA website.
  6. People and animals must be evacuated from the building.
  7. Do not stand on or near slats or the agitation point. If possible, agitate from outside the shed and replace indoor slurry agitation points with external agitation points. Keep in mind that toxic gases are being released even if you cannot smell them, so only enter the shed after at least 30 minutes after agitation has finished. It is important to avoid smoking or the use of naked flames, as slurry gasses are highly flammable.

Slurry Tank Openings

For all other tanks, the first step is to provide safety manhole access covers and a grid underneath. Some older slatted units may not have safety manhole access covers, and the farmer or contractor may have to lift heavy slats. When slats are removed for access, temporary covers or guardrails must be used to protect the opening and warning signs should be put in place. However, this is not an ideal situation and these slats should be replaced with safety access covers.

The design lifespan of most shed components designed to grant specification is about 20 years. Slats and manhole covers need to be replaced before they fail, therefore it is essential that they are checked each year. Examine the slats for sagging, cracking, rust staining and spalling of concrete. 

Never enter a slurry tank because toxic gases and displaced oxygen make it an extremely dangerous environment. Tanks should only be accessed by competent specialist companies who have appropriate equipment (including air monitoring, breathing and lifting apparatus) and who have competent operators (e.g. highly training in entering confined spaces and use of PPE). These companies will always do risk assessments prior to beginning work.

Slurry Tanker & PTO

It is essential that the PTO shaft & PTO stub are fully guarded. According to the Health and Safety Authority, a high proportion of serious and fatal PTO related accidents occur when using slurry tankers.

Based on statistics from the Health and Safety Authority, farming continues to have the highest fatality of any economic activity. Drowning (a particular concern with children) in slurry and asphyxiation (by slurry gases) account for circa 10% of all those killed on farms. Mixing and spreading slurry are high-risk activities. Drowning and gas poisoning together with the potential of crush injuries from machinery are the main risk areas.

While it can be said that children and the elderly are at particular risk of the dangers of slurry, every farmer must proceed with caution when dealing with the substance. According to Teagasc, 10% of deaths in farming and forestry between 2011 and 2020 were slurry related incidents. This worrying statistic sheds light on a health and safety issue that has been present among the farming community for quite some time. 

Moreover, these worries have been “exacerbated” as a result of reports from the Environmental Protection Agency (EPA). The EPA found that many slurry pits operating within the Republic of Ireland failed to meet the standards imposed by the HSA. 

Mary Mulcahy of Ireland Waste Water said that, “the statistics in the EPAs most recent report are stark and they are a testament to the fact that not enough is being done on building awareness of the problems and of support available to uphold standards”. 

“We (Ireland Waste Water) are advocating for a hastening of the pace at which Government and local authorities are addressing these issues, and perhaps more sanctioning for those who don’t abide by the existing guidelines. The way local authorities deal with this issue varies from county to county also – there is not a uniform approach to penalties and sanctions when perhaps there should be. The duty of care cannot rest solely with the homeowner,” she added, “because this is the current state of play, and we can see from this report and others before it.”

As previously mentioned, slurry deaths can arise from drowning or gassing. It can be difficult to determine which is the primary cause of slurry related deaths in Ireland, but it is vital to put measures in place to protect against either cause. It is common for farmers to think that gassing is the main issue, and it comes as a surprise that drowning is such a frequent occurrence.

Farmers are often busy when working around an agitator, and it is possible to lose concentration and step-back into a slurry tank. As slurry is a viscous liquid with 6-8% solids, it is not easy for a person to escape from this situation. Also, the slurry agitator is running in the same vicinity and the possibility of entanglement arises.

The safety message from this scenario should be clear: 

  1. Prevention is the issue. 
  2. Have safety grids and barriers installed to prevent falling into slurry.
  3. Maintain high vigilance when placing slurry agitators into position. 

The HSA has presented a comprehensive list of precautions that should be followed by any individual who is involved in the handling, maintenance or other use of slurry. They are as follows: 

  • Open slurry tanks should be protected by an unclimbable fence or wall at least 1.8 metres high, with locked gates. 
  • When the tank has to be emptied, consider having an adequately constructed access platform with safety rails.
  • Covered or slatted tanks require access to manholes that children cannot open easily. Fit a safety grid below the manhole to give secondary protection. All slurry tanks should be adequately fenced.
  • Evacuate all livestock and make sure no person or animal is in or near the building.
  • Do not allow slurry to rise within 300 mm of the slats or tank covers.
  • Avoid smoking and naked flames as the gas mixture can be highly flammable.
  • Never enter a tank for any reason – gases can build up and remain in partially emptied tanks above the slurry.
  • Never enter the slurry tank or any confined space unless you are wearing suitable breathing apparatus and/ or a harness attached to a lifeline controlled by at least two other adults positioned outside the area.
  • Put up warning signs to warn of the dangers when working with slurry.
  • Scrape holes on outdoor lagoons should be adequately protected.
  • Cover all slurry tank manhole openings.
  • Beware of the risk of back injury if you need to lift slats in the shed.
  • Agricultural contractors must be aware of the dangers of working with slurry and should ensure that they work safely at all times.
  • Use outdoor agitation points where possible – one lung-full of slurry gas can kill.
  • Only agitate where there is good air movement.
  • Evacuate and ventilate before you agitate.
  • Open all doors and outlets to provide a draught.
  • Avoid vigorous agitation in confined spaces.
  • At least two people should be present and should stand up-wind.
  • Keep all people away from the agitation point for 30 minutes after starting agitation.
  • Keep children and elderly persons away from the area when agitating.
  • Never stand over slats or near tank access points when agitation is in progress.
  • Guard the PTO on the slurry tanker and agitator– do not use unless correctly guarded. A high proportion of PTO entanglements occur when using slurry tankers.

Findings published by the HSA in 2020 decree that the first 30 minutes of mixing are the most hazardous. As mixing continues, the quantity of slurry gas released falls off. However, each time the pump is repositioned to mix another part of the tank, gas concentration rises again. Ensuring that your slurry pump is operating correctly is imperative for anyone who intends to work with slurry. Wherever possible, slurry pump agitation should be controlled from outside the building, otherwise operators must leave immediately as pumping starts. 

Slurry pumps that are designed to allow the PTO shaft to remain attached to the tractor when the pump is being transported have a high centre of gravity. It is essential that the two lower lift arms on the tractor are properly latched and locked into the two brackets on the slurry pump linkage frame before the top link or PTO (Power-Take-Off) shaft are attached. When not in use, it is very important that the pump is parked using the support legs on a solid, evenly flat surface. In addition to an adequately working slurry pump, we would advocate that gas concentration meters should also be available. 

Ultimately, spreading slurry is potentially one of the most hazardous activities that a farmer undertakes, with the two main risks of drowning and gas poisoning outlined above. Farmers should not take unnecessary risks and follow simple steps to ensure their own safety and the safety of those around them. Most farm accidents are preventable and incidents involving slurry are no exception. Following these precautions is the best way to keep you, your workers and the public as safe as possible. Prevent accidents and save lives by always following the safe system of work prescribed by legitimate agricultural based bodies.